Magnetic tape storage systems are widely used in computer systems for storing and retrieving large amounts of data. A typical system will be described, but the following description should not be taken to encompass the variety of systems available. Current systems typically read and write from parallel tracks on the tape which vary in number based on the design of the system. Each track of the head has a read and a write magnetic transducer (head) arranged in tandem so that the data written by the write head can be verified by the read head. The head pairs may be alternated so that one set of the tracks are written and read when the tape travels in the one direction and the other set is used when the tape is moving in the opposite direction.
Some tapes are written with magnetic servo information thereon to allow positioning the heads in relation to the tracks. All tapes have a magnetic noise floor which is present even when the tape is erased. Therefore, even a tape with no data recorded thereon will generate a noise signal in the read heads and tapes with servo information will also generate signals corresponding to servo information.
For high density recording the tape must be precisely positioned and tensioned as it moves across the head assembly. The tape is typically supported and positioned by support surfaces, for example cylindrical rollers or posts or guides disposed on each side of the head. The support surfaces are positioned behind the head to form the wrap angles which are the angles of the plane of the tape with respect to the air bearing surfaces of the head. Precise wrap angles are necessary for optimum performance.
U.S. Pat. No. 3,123,811 (Mutziger) describes a tape system which has pairs of physically separate heads disposed in a confronting position. The tape is directed through a capstan and pinch roller combination and sequentially over the first pair of heads. The tape then loops around a roller in 180 degree turn and, passes sequentially over the second pair of heads. The problem being addressed by Mutziger is that there is a need to synchronize the signals read by the first pair of heads with the signals from the second pair of heads. One source of error in the described system is, of course, in the precise placement of the heads. Mutziger solves the problem by positioning an eccentrically mounted tape guide between the head pairs. The tape travel between the heads in the first pair is straight. The eccentric tape guide is used to deflect and, thereby, lengthen the tape path between the heads in the second pair. The eccentric tape guide is rotated to adjust the precise length of the tape between the second pair of heads to synchronize signals being read from tape. After desired adjustment is obtained, the eccentric tape guide is locked in place to prevent rotation.
Components and methods which increase the precision of the wrap angle are needed in the art.